Composite panels, such as 5 stringer panels that can be used in aircraft and other products, are tested during the research and development phase of a project and must be tested during a certification process before they can be used in an aircraft or similar product. Currently, these 5 stringer panels are tested using one of three common methods. Testing of full 5 stringer panels, modeling and analyzing 5 stringer panels using computer simulation, or testing smaller sample panels (coupons) using a single tension or compression load and extrapolating the results back to a full 5 stringer panel. However, each of these current methods has its own drawbacks and inefficiencies.
For example, it can cost millions of dollars a year to manufacture and test full composite 5 stringer panels. While testing of at least one 5 stringer panel is necessary for certifying a composite structure prior to the structural design being used on an aircraft, each full 5 stringer panel can cost up to $1,200,000 and can take up to 6 months to fabricate and test. In addition, multiple 5 stringer panel tests need to be performed on new composite technologies in order to obtain a statistically meaningful data set across the range of thicknesses and layups being considered for use. Because of the long lead time and high cost, testing multiple possible designs and/or materials for a 5 stringer panel can be cost and time prohibitive and can possibly lead designers to settle for a panel design that is good enough for a particular design application instead of a panel design that is the best or optimized for a particular design application.
In addition, using computer modeling of 5 stringer panels currently does not provide the accuracy required in the research and development phase of projects. For example, current computer models cannot reliably predict failure load, failure mode, and damage trajectory. The current reliability of computer models is approximately 70-80%. That means that 20-30% of the time, this analysis methods fail to predict the results. This can result in design changes that affect program costs and schedule by pushing back final design and loads 6-12 months and spending more money to manufacture additional 5 stringer panels for testing every time this happens.
Finally, testing coupons (i.e., small sections of a material to be used in a 5 stringer panel) has been utilized in an attempt to reduce overall costs associated with new composite materials. Unfortunately, the existing coupon test method loads the coupon in a uni-axial fashion and doesn't load the material in a way that is representative of the 5 stringer panel conditions. Because of this, current coupon test methods fail to predict the performance of the 5-stringer composite panel reliably and accurately.
Therefore, there is a need for a material test method and panel design method that is low cost, fast, accurate, and reliable.